This invention relates to an ultra-fast imaging method and apparatus.
Conventionally, ultra-fast data acquisition has been discussed in the following references:
(1) Japanese Journal of Magnetic Resonance in Medicine, Vol. 7, No. 2(1987), pp. 3-24
(2) Magnetic Resonance in Medicine, Vol. 10(1989), pp. 227-240
The reference (1) discusses generally ultra-fast data acquisition systems and explains in Paragraph 2 methods of reducing the number of times of measurement. It introduces various methods of obtaining at an ultra-high speed a single image. All the data required for reconstruction are acquired at once in the ultra-fast data acquisition. The data corresponds to those of k-space. Each of methods for ultra-fast data acquisition in the reference (1) are different from how to trace their own k-trajectory on which the data are put. If all the data of k-trajectory necessary for reconstruction cannot be obtained at once, ultra-fast data acquisition cannot be made but the reference suggests to carry out acquisition dividedly to obtain necessary k-trajectory.
The reference (2) discloses an example of actual ultra-fast data acquisition, and illustrates the result of ultra-fast data acquisition by the use of a sequence which is a kind of an echo-planar method using pulse gradient fields referred to as "BEST". Unlike the reference (1), the reference (2) teaches various innovations on hardwares such as the technique of keeping homogeneity of an electrostatic magnetic field necessary for practical ultra-fast data acquisition, counter-measures for eddy currents in an RF coil by means of switching of gradient magnetic fields, and so forth, and discloses the result of practical data acquisition of the abdomen and the heat and imaging of the data acquired.
To obtain a sufficiently wide image by executing practically such ultra-fast data acquisition, various hardware limitations are imposed on an imaging apparatus. The dimension of the region which can be measured in ultra-fast data acquisition depends on the intensity of a readout gradient magnetic field as a vibrating magnetic field, on a switching speed (a synchronization speed of vibration) in the imaging apparatus, the resolution of the image and sequence for generating magnetic resonance signals. Therefore, the imaging apparatus becomes more expensive. The imaging apparatuses which have gained a wide application at present and which repeat acquisition for one region are not provided with hardwares necessary for obtaining a sufficiently wide region in ultra-fast data acquisition or in other words, a readout gradient field generator equipped with a sufficient intensity and a sufficient switching speed.
Another prior art reference related with the present invention is JP-A-63-105748. This reference discloses a spin-echo method which measures only the region which is desired to be visualized. This spin-echo method effects, for example, 90.degree. slice selection by a first RF pulse, phase-inverts by 180.degree. the slice crossing the former slice by a second RF pulse and images the crossing regions.